1. Field of the Invention
The present invention relates to a photoresist stripping solution. In particular, the invention relates to a photoresist stripping solution to be used in a process of producing liquid-crystal panels and a process of producing semiconductor chip packages.
2. Description of the Related Art
A liquid-crystal display such as TFT-LCD has a structure of liquid crystal sandwiched between opposite glass substrates, in which, in general, a TFT (thin-film-transistor) and a pixel electrode (transparent electrode) are formed on one glass substrate and an alignment film is superposed thereon to cover the entire surface of the substrate, while a color filter, a transparent electrode and an alignment film are laminated in order on the other glass substrate, and the glass substrates are positioned oppositely to each other with their alignment film-coated sides facing each other. In this case, the TFT is more bulky than the pixel electrode on the one glass substrate, and therefore the thickness of the liquid crystal sandwiched between the opposite glass electrodes could not be uniform, or that is, the thickness of the liquid crystal in the site corresponding to the TFT may be thereby smaller.
Accordingly, a method for making the thickness of the liquid crystal uniform has heretofore been employed, which is as follows: After a TFT is firstly formed on one glass substrate, a transparent insulating film (e.g., acrylic transparent film) is formed on the entire surface of the glass substrate to completely cover the TFT, thereby absorbing the TFT height difference to planarize the surface of the resulting substrate, and a pixel electrode (transparent electrode) is then formed on the surface-planarized acrylic transparent film, and thereafter an alignment film is superposed on the entire surface thereof.
The pixel electrode (transparent electrode) is formed as follows: A transparent conductive film is formed on an acrylic transparent film by sputtering or the like, a photoresist is uniformly applied onto it, and the photoresist is selectively exposed to light and developed to form a photoresist pattern, then the transparent conductive film is selectively etched through the photoresist pattern serving as a mask to form a pixel electrode (transparent electrode), and thereafter the photoresist pattern is stripped with a stripping solution.
Accordingly, since the stripping solution is brought into direct contact with the acrylic transparent film in the treatment of stripping the photoresist pattern, it is indispensable that the stripping solution should not have any negative influence of swelling or coloration on the acrylic transparent film. If the acrylic transparent film is swollen, then it may cause a problem in that the transparent electrode formed thereon may be inconveniently peeled; and if colored, then the acrylic film may lose its transparency.
On the other hand, in a process of fabricating semiconductor chip packages, a technique of producing wafer-level chip size packages (W-CSP) has become employed recently, in which ultra-small size, wafer-level chips are packaged all at a time for satisfying the recent multi-layer microfabrication technology in producing semiconductor devices.
The process of producing W-CSP comprises, for example, forming a conductive metal film (e.g., thin copper film) on a substrate such as a silicon wafer having a passivation film (insulating film) thereon by sputtering, providing a positive photoresist pattern on the thin copper film, and etching the thin copper film through the pattern serving as a mask to form a copper rerouting or re-wiring pattern. One or more layers of the insulating film/rerouting pattern are formed as a single-layer or multi-layer structure.
Next, a photosensitive dry film of a negative photoresist is stuck to the substrate under heat and pressure, then this is selectively exposed to light and developed to form a thick-film photoresist pattern (photocured pattern), a copper post (bump) is formed in the area not having the photoresist pattern, by plating, and thereafter the photoresist pattern is removed with a stripping solution. Next, this is sealed up with a sealant resin to cover the entire surface of the substrate so as to completely cover the copper post, and thereafter the upper part of the sealant resin and the upper part of the copper post are all cut off. A conductive terminal (copper terminal) is soldered to the top of the thuscut and exposed copper post, and thereafter the wafer is cut into individual packages.
In the process of producing packages, the negative photoresist pattern (photocured pattern) is more difficult to remove than the positive photoresist pattern and, in addition, since it should be thick as used for copper post (bump) formation, and therefore it is further more difficult to remove by stripping. Accordingly, it is desired that such a hardly-removable thick negative photoresist could be removed more easily. In addition, it is also desired that the metal (copper) is damaged little by the removing treatment.
Most photoresist stripping solutions that have heretofore been used in production of liquid-crystal panels and semiconductor devices are water-based photoresist stripping solutions that comprise a polar solvent, an amine (including quaternary ammonium salts) and water (e.g., see Patent References 1 and 2). However, these stripping solutions contain water and therefore their damage to metal materials is inevitable, and, in addition, there are other problems in that they have some negative influences of coloration and swelling on acrylic transparent films that are used in liquid-crystal displays.
Patent Reference 1: JP-A 2001-215736
Patent Reference 2: JP-A 10-239865